WASHINGTON (CNN) --Sources close to the Washington-area sniper investigation are giving more details of the communications between police and the person investigators suspect is the sniper.

•One official said investigators received a "communication" from the Richmond, Virginia, area early Sunday morning instructing them where to find a letter.

•The letter police believe to have been left by the sniper behind the Ponderosa Steakhouse in Ashland, Virginia -- the scene of Saturday night's sniper shooting -- contained a telephone number. Police were instructed to call the sniper at that number to establish communication.

•The official said following the discovery of the letter, there was a "heavy resource commitment" and "robust federal presence" in the Richmond metro area.

•Police said the number was for a residence and they felt that the sniper had inadvertently transposed the last two digits of the telephone number. When the numbers were reordered, the phone number led to a business, which investigators thought was a more likely point of contact.

•Authorities had both the original number and what they believed to be the intended number routed to the sniper task force offices in Rockville, Maryland.

•Montgomery County, Maryland, Police Chief Charles Moose stood in front of television news cameras Sunday night and announced: "To the person who left us a message at the Ponderosa last night -- you gave us a telephone number. We do want to talk to you. Call us at the number you provided."

•Investigators believe the sniper called the number -- now routed to the task force -- Monday morning but used some kind of device to disguise his voice, according to the source. The source would not say whether the caller appeared to be using a tape recorder or some sort of voice-altering device.

•Moose came out again before news cameras Monday afternoon, saying, "The person you called could not hear everything that you said. The audio was unclear. We want to get it right. Call us back so that we can clearly understand."

•On Tuesday, Moose told the gathered reporters that authorities had received another "communication" and that they "will be responding soon." Moose also released information about the Ponderosa letter, because he said authorities believed its contents were being misreported.

"We recognize the concerns of the community and, therefore, are going to provide the exact language in the message that pertains to the threat. It is in the form of a postscript: 'Your children are not safe anywhere, at any time,'" Moose said.

•Another official said that the letter found behind the Ponderosa restaurant contained several demands and a timeline for officials to act. If officials failed to act, the source said, the letter threatened other attacks.

•Moose returned to the cameras Tuesday night and read a new communique to the letter writer:

"In the past several days, you have attempted to communicate with us. We have researched the option you stated and found it is not possible electronically to comply in the manner that you requested," he said.

"However, we remain open and ready to talk to you about the options you have mentioned.

"It is important that we do this without anyone else getting hurt. Call us at the same number you used before to obtain the 800 number that you have requested.

"If you would feel more comfortable, a private post office box or another secure method can be provided.

"You indicated that this is about more than violence. We are waiting to hear from you," Moose said.

•A source close to the investigation said the letter found Sunday demanded $10 million. It was not immediately clear whether that $10 million demand was what Moose referred to when he said it was impossible "electronically" to comply with the sniper's wish.